I’m very worried the child’s father is going to get custody. We all have read about his track record and what a “stellar” 
member of society he is.
Finances, retirement, energy level, and potential health problems all affect us as we age. Also, just the generation gap, itself, can cause friction between parents and children when the age difference is beyond a certain number of years.
For example, my father thought any male who didn’t have a military haircut had “long” hair. He would give some of my dates a really hard time about that. In my opinion, they didn’t have long hair at all. Music, fashion, etc. can lead to huge arguments. My dad encountered that type of thing with his parents. Their Beatles records made my grandmother nervous. My grandfather was of the opinion that the long-haired boys from Britain screwed up morality in our country. That generation gap was only 20-30 years. When it goes beyond that, there is a good possibility you and your great grandson aren’t going to like each other at times.
I know you’ve had these same concerns about raising your great grandson. If you feel you are prepared to handle these things, I say go for custody.
